Animals possess a highly sophisticated mechanism of storing energy in adipose tissue inside their bodies. However, in humans it has been clarified that adipocyte (fat cell), which composes the body fat (adipose) tissues, development and the extent of subsequent fat accumulation are closely associated with the occurrence and advancement of various common diseases (e.g., type-2 diabetes, coronary artery disease, and hypertension) resulting from obesity. Recent exciting progress in clinical and biochemical studies of adipocytes has rapidly clarified the functions of adipocytes and adipose tissue. Interesting findings are the function of white adipocytes as "secreting cells" and the molecular mechanism undelying adipocyte differentiation at the transcriptional level in relation to nuclear receptors. Consequently, the adipose tissue is being targeted for the prevention or treatment of many common diseases. In this review, I will focus on recent information on characteristics of adipocytes and the relationship between obesity and common obesity-related diseases. diseases.